Methane has been decomposed over supported metal catalyst particles at temperatures of about 300° C. to 500° C. to produce hydrogen and carbon. A goal of the process is to obtain hydrogen gas uncontaminated with carbon monoxide. Metals such as iron, nickel or palladium deposited as fine particles on high surface area oxides of aluminum, cerium, molybdenum, silicon, thorium or zirconium have been evaluated as catalysts. Certain zeolites have also been used as catalyst supports. Catalysts formed of nickel particles deposited on alumina, ceria, silica, or zirconia supports have attracted attention. The supported catalyst is confined in a heated flow-through reactor and methane, usually diluted with nitrogen, helium or the like, is passed over the catalyst at a suitable space velocity. Some methane decomposes to hydrogen and carbon. Hydrogen exits in the exhaust stream, also containing un-decomposed methane and diluent; and fine carbon particles deposit on the catalyst. Sometimes the metal oxide carrier also promotes the formation of carbon monoxide.
Deposited carbon gradually degrades the performance of the catalyst, but it can be re-generated by passing hot steam over the catalyst bed to oxidize the carbon to carbon dioxide and form more hydrogen. The product gas stream is a mixture of hydrogen, CO2, and unreacted steam.
Thus, for continuous operation, the overall process comprises two-steps; hydrogen is produced in step one, and hydrogen and CO2 are produced in step two. The process has been conducted using two parallel catalytic reactors with one bed catalyzing the decomposition of methane and the other bed being treated with steam for carbon removal and catalyst reactivation. In another practice mode, a single bed is alternately and cyclically contacted, first with methane and then with steam, to produce the hydrogen and CO2 product streams. As observed, the methane content of the feed stream is not wholly decomposed and often the product stream contains some CO due to the use of oxygen-containing catalyst supports.